Hydrofluoroolefins (HFOs) have been adopted as replacements for high-GWP hydrofluorocarbons (HFCs) across multiple applications including foam blowing, refrigeration, and aerosols, but their atmospheric degradation and climate consequences remain uncertain.1,2 Here, we use the GEOS-Chem 3-D chemical transport model, supported by AtChem2 box-model simulations, to develop a complete representation of the atmospheric chemistry and fate of HFO-1234ze(E) and its key intermediate product, CF3CHO. The model includes newly measured CF3CHO photolysis quantum yields to form fluoroform (HFC-23), the recently identified chemical pathways of HFO-1234ze(E) ozonolysis and CF3CHO reversible reaction with HO2, and explicit wet and dry deposition parameterisations.2,3 Using observationally constrained global HFO-1234ze(E) emissions of 35 Gg yr-1, simulated HFO-1234ze(E) surface mixing ratios agreed well with observations at 8 Advanced Global Atmospheric Gases Experiment (AGAGE) sites across the globe.4 We find that 99.6% of HFO-1234ze(E) is removed by reaction with OH, with the remaining 0.4% lost to ozonolysis. Sensitivity tests for effective Henry's law constants (KH*) spanning 10 - 106 M atm-1 show sensitivity of \ce{CF3CHO} fate to KH* up to 104 M atm-1 and saturation at higher KH*. Using an upper bound of 105 M atm-1, we find deposition accounts for about 55% of total CF3CHO loss in GEOS-Chem (17% dry, 38% wet), with a further 25% lost to photolysis and 17% to reaction with OH. The reversible reaction with HO2 contributes just 1% to net CF3CHO loss due to rapid conversion of the reaction products back to reactants. We find an overall GWP100 for HFO-1234ze of around 13, with CF3CHO photolysis to HFC-23 contributing 5.4. We also estimate a maximum potential formation of 6 Gg yr-1 of trifluoroacetic acid (TFA) from wet-deposited CF3CHO, suggesting a potential unrecognised TFA source from atmospheric degradation of HFO-1234ze(E).